Lithographic plate and method of making the same



Iva/mm 'w mw v a Nov. 17, 1925.- (1,562,324 W. GRASS I LITHOGRAPHIQ PLATE AND METHOD OF MAKING SAME ori inal Filed May 14 192.0

hid/ mm Gama Patented Nov. 17, 19 25, f

, unrren STATES PATENT OFFICE.

wILLrAivi GRASS, or WEEHAWKEN, NEW JnnsEY, Assrenon To GRASS PATENTS conronATIoN, or NEW YORK, N. Y.

L'ITHoeRArHIc PLATE AND METHOD or MAKING THE SAME.

Application filed May 14, 1920, Serial No. 381,386. Renewed April 29, 1925.

To all whom it may concern:

Be it known that WILLIAM GRASS, citi zen of the United States, residing at 722 Park Avenue, Weehawken, in the county of Hudson and State of New Jersey, has invented certain new and useful Improvements in Lithographic Plates and Methods of Making the Same, of which the following is a specification.

My invention relates to lithographic plates for printing by either the offset or direct method, and to-an improved method or process of producing such plates by which the action of the etching agent is limited and prevented from spreading through the gra n of the-plate beyond the parts of said grain which-are designed to be removed. I

This process and the result thereof has relation to that described in the Patent No. 1,155,352 granted to Jacob Grass, October 5, 1915, but it is to be understood that" my present invention can be used in connection with such patented process or variations thereof and also in connection with or as a "part of other processes in which it .is,

r 2 wherem thest pple eflfect represents the adaptable.

The main idea and feature of said pat ented process is the production-of a lithographic printing plate in which the greasy ink-holdmg lines and dots are not laid upon the extreme top surface of the grain of the. plate but are in etched recesses slightly below the top surface.

This has been described as intaglio butsuch descriptiongis misleading because said etched plate -is quite different from a true intaglio, such as a copper plate, and could not be printed from in the same way.

The etched plate produced according to the present improvementis cut away, where it is to take ink, to the slightest possible depth, which may in'practice be only to such extent as to destroy or remove the water holding and ink repelling grain.

By the present improvement the etching action is modified ,and controlled so as not to go beyond the intended boundary and not to an undesirable depth and so asnot to work laterally into the grain and colloid coating which is not to be removed. 7

This last mentioned beneficial result prevents the degrading of the outlines and leaves the boundaries between the etched and grained parts very sharply defined, and the sharpness of the printing as Well as the durability of the plate are enhanced.

. To .more easily comprehend the invention I herein disclosed I have appended herewith three diagrammatic-views tojhelp illustrate just the actiontaking place in the carrying out of. this process. U

.' Fig. 1 represents a sectional enlargement of a plate havin a rained surface and coatsion of the'light rays at the defined edges. 7

of the design causing what is known as halation.v

- This halation efiect produces a variable hardening of the film by slightly undercutting the edges of the design, a graphic representation of this action would be like Fig.

there is first produced a grained plate cov' j "ered by a colloidal film that is acid and etch resisting after exposure to light. This colloidal film when exposedto lightthrough a transparency acquires varying de es of. hardness, beginning first on the lly' exposed surfaces and. by continued exposure the light penetrating throu h the clear and semi-opaque portions of t e transparency produces the halo mentioned around the edges of the design and causes a mild hardening ofthe colloid in these areas;-

This semi-hardened colloid" can be removed by adjusting the physical density of the etching fluid and the time in which the etching fluid is permitted to act on the plate.

Theremust also be a coordinating action between the lighttime, the colloidal hardness, density of etching-fluid, and time. of etch so that the acid will eat away the halationhardened colloidiand the metal under it until the boundary of the etcheddesign cmresponds to the boundary of the transparency design. L y i Y An etching fluid having the characteristics to produce the results desired is made by preparing a. solution of ferricchloride in water at 43 Baum, reduced-to a neutral condition by the addition of a suitable alkali,

such as soda bicarbonate, to produce a nonwater holding grain of the plate and the halation hardened colloid and produce inkholding recesses of almost imperceptible depth. i

When using ordinary etchingfluids on zinc plates a galvanic and heating action is set up resulting in a deposition of metallic salts in the bottoms of the. etched areas which deposits greatly'diminish the ink-re-' ceptive qualities of the plates. But by neutralizing the ferric chloride the galvanic action and heating are almost entirely counteracted and the. deposition of foreign matter in the etchedareas is greatly reduced,

" and thereby markedly superior results are obtained in the uniformity of the good printing quality of the plate and the durability of the same, due to the properly balanced etching fluid and the accurate etching to just the required depth and area and to'the greatly lessened deposits of metallic salts in the bot toms of the etchings which leaves the pure,

metal exposed for the reception of the ink.

shown the area, 4 representing that covered by the dot 2, after etching and is seen to be The solution need not be strong enough i .to etch the solid metal but is sufficiently.

strong to destroy the. grain. of the plate where it is desired to remove it. g V

The density of the solution is to be such that it will not soak or spread into the grainv which is not to be etched, and it should be just acid enough to remove the exposed grain, as to which the usual etchers precautions are to be observed; and these results I have sucity of the etching fluid in relation to the;

cessively accomplished with the'propor tions of ingredients above described; But some-- what varied proportions may give good results under conditions which I have. not enumerated or encountered. i

. A particular feature of this invention re- 'h-ardness of the film, time of etch, etc., that the halation hardened portions of the film .-.are\removed during the time of etching to.

thereby bring the boundaries of the etched design exactly coincident with the design on r dots.2 are each one inch in diameter, the

light passing through the transparency 1 gradually-hardens the colloid to the fulldegree desired on all portions around the dots 2 but while passing by the edges of the dots 2' there is'a slight diffusion oflight under the edge of the dots causing the'slight halo 3 Fig. 2 represented by the stipple just under the edges of the dots. Fig. 2 shows the full hardening of the film over theexposed areas represented by the heavy stipple and the partial hardening just under the edges of the dots by the lighter stipple which is caused by the halation referred to. If, now, the etching fluid did not remove the semi-hardened colloid directly under the edge of the dot 2, the etched dot on the plate would be slightly less than one inchin diameter, which in a half-tone print would change the tone value'of the light effects by showing too much light around the dots.

r The balancing of my eching fluid is such that during the time period this semi-hard ened portion of the colloid directly under the edges of the dots willbe eaten awayas well as the grained surface of the metal plate directly under it so that the finished etched dot on the plate will be of the same diameter as the dot on the transparency. r

This is represented in Fig. 3 wherein is the same size as the dot 2 on the transparency.

every sensitivefilm or emulsion and gives a false translation of the copy unless it is removed. The etching acid is given a Baum density and a physical etching quality that in ,a given time will remove this partial hardened colloid and always produce dots and other shapes exactly the same size as the positive copy. 7

, After the etching is finished the etched surface is treated with dilute hydrochloric acid or other means and the loosened foreign matter left by the etching is removed with wool, and the plate dried, after which litho- 7 graphic ink is rubbed, worked or rolled into the etched parts of the plate. Before inking the plate the film may be dyed, not as a necessary step but to enable the design, to "bef v more easily inspected as to erfection before "proceeding furt er, so t at time and labor may not be we ted on a plate which vent oxidation, and the plate is then ready to be used in the printing'machine.

In this machine the normal grained sur face of the plate is dampened with water so" that it will reject ink, the water being rejected by the ink or equivalent material in the etchings; then an inked roller is passed over the plate so as to ink the etchings ready for printing, the ink being repelled by and not "taken .on the dampened high surface; and then the paper, tin or other material on which the printing is to be done is irn' pressed on the plate. In the case of off-set printing the impression is first made on a rubber blanket in a known. manner and thence transferred to the. material to be rinted. I

When alithographic plate is produced according to the said patent, or when it has been produced by the use of the improved etching bath above "d'esc'ribed,I do or may proceed as'follows for the removal of the deposited salts in the first case or for the more complete removal of any remains of said salts in the second case, the purpose being in either case to expose as fully aspossible the solid metal of the plate in the etchings: I prepare a' bath consisting of about eight ounces of water in which are dissolved one, and one-half ounces of hydrochloric acid, and I immerse in this bath the etched plate from hich cleaned away. I action of the three-quarters of a minute to one minute. This bath acts in the etchedrecesses so as to partly dissolve and loosen the metallic or other deposits.

which the plate is dried when it will be 5 found that the These can then be easily removed with cotton wool, and turpentine or the llke, after etched surfaces show an exposure of pure zinc which is 100' per cent receptive and retentive of grease (Ink). The important part in printing on the press 1s the true retentive qualities of case on the pure and clean. metal, when a egree of imp i y cent grease sensitiveness in a like amount, and the parts'receive inkin varying quantities.

the film has not been The plate is subjected-to the last mentioned bath for fromv to the action of an etchlng ferric chloride and a neutralizing agent, and

- exists; that degree of-impurity r educes the 100 per I The deposits may. be removed after drying but at a greater I'lSk of injury to the etched surface as more friction antll effort is required to remove the materia. 1

It is usually or often desirable to'give to the normal grained or high surface of the plate a'strong surface etch with phosphoric and chromic acid, in a known manner. This is not strictly an'etching, though-it is usu- .a'lly so described, but causes the normal surface to be strongly receptive of water so as to be thoroughly repellant to ink. The last mentioned bath and cleaning of the plate will prevent said surface etch from creeping v around under the ink through the deposited salts which would, otherwise be in the etchings, which "would undermine the ink and would render the etchings less receptive of the ink, softhat after a number of impres sions the print would gradually become gray and not of the desired full and distinct color. I

This would be because the proper amount of sensitive color (ink) cannot be applied,

by the inking of the plate, to be transferred to the material to be printed, or to the blanket. i

Inprinting, a little chromic acid is added the grainedsurface of the plate in order to continually renew. the grease-repelling action of said surface, and this acid excepting for the above cleaning, would continually act to undermine the ink and result in the 'want of suflicient, ink and color in the print- .methodand means known to me for successfully carrying out my improvements, but it will be understood that variations can be made therein without departing from the spirit'of the invention.

What is claimed is:

1. In a method ofproducing a-printing surface on a metal lithographic plate, etchto the dampening water which LS applied to from the etchings the latter may become ing the plate and removing the surface thereof in exposed and" defined places by subjecting'it, while partly protected by a film, to the action of an etching bath containing a'neutralized acid, andcontaining in addition an etching; acid.

2. In a method of producing a printing surface on a metal lithographic plate, etching the plate and removing the surface-thereof in'exposed and defined places by subjecting' it, while partly protected by a film, bath containing made acid by nitric and hydrochloric'acids.

3. Ina method of producing a printing surface on 'a metal lithographic plate, etching the plate and removing the surface thereof in exposed and defined places by subjecting it, while partly protected b to the action of an etching ,bath containing ferric chloride neutralized by soda bicarbonate and made acid by nitric and hydrochloric acids.

4. In a method of producing a printing surface on a metal lithographic plate, etching the plate, while partly protected by a film, in an acid bath, and removing the surface thereof'in exposed and defined places,- then removing said film,-'then loosening and more or less dissolving the deposits in the etchings produced by said etching bath, and then removing said deposits.

5. In a methodof producing a printing surface on a metal lithographic'plate, etching. the plate, while partly protected by a film, in an acid bath, and removing the surface thereof in exposed and defined places,

then removing said film, then loosening and more; or less dissolving the deposits in the etchings produced by said etching bath, and then rubbing the plate with a cleaning materiaL' J ,p

6. In a method of producing a printing surface ona metal lithographic plate, etching the plate, while partly protected by a film, in an acid bath, and removing the surface'thereof in exposed and defined places, then removing said film, then loosening and more or less dissolving the deposits in the etchings produced by said etching bath, andi .then rubbing the plate'with turpentine.

' 7. A lithographic printing'plate having -a top or normal ink-re elling surface and inkreceiving etchings s ightly below" said surface, in which etchings the' pure. metal of surface, in which etchings the pure metal of the plate isfexposed by an acid bath and subsequent cleaning.

10. In a method of producing'a printing surface on a metal lithographic plate, coating the plate with a sensitized emulsion, ex% posing it to light under a transparency, to harden vportions of the film, removing the unhiardened parts of the film 'from the plate surface, subjecting. the exposed plate surfaces to the actionof an etching fluid to remove theexposed surface, said fluid being so balanced that during the given time of .etchingthe uncovered areas of the plate, the

fluid will also remove certain semi-hardened. portions of the emulsion' lying around the edge of the design being etched to thus pro-- duce an etched area from which the surface of the-plate has been removed exactly coinciding with the design on the transparency. In testimony whereof I aflix my signature.

- WILLIAM GRASS. 

